Airguns are used for seismic exploration. They are impulsive energy sources which are triggered to discharge a powerful blast of pressurized gaseous fluid from the airgun. This pressurized gaseous fluid usually is compressed air. However, other pressurized gaseous fluids can be used. Thus, the term "pressurized gaseous fluid" as used herein is intended to include a pressurized gas and a pressurized mixture of gases, for example, compressed air, compressed Nitrogen, compressed Carbon Dioxide, and compressed gaseous products of combustion.
The surrounding ambient "water medium" as described herein is intended to include salt water, fresh water, water-filled muddy areas and watery marsh or swamp areas. The powerful blast of pressurized gaseous fluid issuing from the airgun through the discharge port suddenly transfers energy into such a surrounding water medium for generating seismic energy waves which are propagated into the Earth for providing seismic exploration data.
To achieve deep penetration of seismic energy into the Earth and to provide more definitive seismic data, it is desirable to maximize the transfer of energy from the blast of gaseous fluid into the surrounding water medium and also desirable to maximize peak pressure of an initial pressure pulse generated by this blast relative to peak pressure of any secondary pressure pulse created in the water medium subsequent to the initial peak pressure pulse.